Operations with various optical channels in an optical network are usually performed by optical equipment pieces, such as OADM (Optical Add Drop Multiplexer), ROADM (Reconfigurable OADM), optical switches WSS (Wavelength Selective Switch), etc. The basic functions of the optical equipment handling optical channels are as follows: passing some of the received optical channels through the equipment without changes, dropping some of the received optical channels and adding some new optical channels. For performing the basic functions optical equipment/device must be able to block one or more optical channels from passing through the device.
Usually, the blocking function is performed using optical filters. Another accepted way to block one or more specific optical channels is to accomplish a pair of actions: de-multiplexing and multiplexing performed so that the specific “unnecessary” optical channels are ignored (not multiplexed) and therefore not included in the group of channels outgoing from the device. The disadvantage of these known blocking operations lay in the non-perfect character of existing modern filters, which (when blocking a channel) usually block/cancel about 40% of the bandwidth surrounding the channel. Such an effect is negligible when spacing between channels is quite large and there is no strong need of compressing the channels and saving the bandwidth. However, bandwidth becomes more and more significant so that a shortage of bandwidth starts to become a problem for providers of modern communications (especially in high rate communication systems). In view of that, the use of current optical filters in high bit rate systems seems more and more problematic, especially for blocking optical channels.
It should be noted that there are some known technologies of suppressing optical signals for security purposes. For example: U.S. patent publication 2010196015A describes a technique for securing data transmission via an optical communication line comprising an optical fiber extending between a first network element and a second network element. The technique described comprises conveying a first optical signal carrying data via an optical fiber from a first network element towards a second network element at a predetermined optical wavelength, and conveying a second optical signal at the same predetermined optical wavelength via the same fiber in the opposite direction. This creates within the optical fiber a combined optical signal such that combination of the first and second optical signals is adapted to hamper an unauthorized non-intrusive extraction of the first optical signal from the combined optical signal.
The presently used filters do not seem to provide an adequate solution for accurately blocking an optical signal of a specific channel in modern optical equipment, such as ROADMs.